This project will complete analysis of a carefully controlled, large scale field experiment designed to evaluate the extent to which interviewer training and supervision can effectively improve the quality of health survey estimates used in health services research. Specifically, analysis of tapes of interviews will be studied to pinpoint the kinds of interviewer behaviors that produce interviewer effects on data. In addition, overall analysis of interviewer effects and ways to reduce them will be extended to focus on two key groups of importance to health services reseatch: the aged and the less educated. The results of this phase of the project will produce tqo benefits for health service researchers. First, the work is expected to produce specific suggestions to improve the content of training and supervision of interviewers. Second, the project will provide specific guidelines to those planning health surveys regarding the extent to which increasing investments in interviewer training anf supervision will lead to increased precision of survey estimates for various kinds of measures and for various populations.